Diagnostic imaging in the medical field is an indispensable medical technology in view of early detection of lesions, preoperative diagnosis, postoperative follow-up diagnosis and so on. Diagnostic imaging methods widely used now in the medical field include CT (computed tomography), MRI (magnetic resonance imaging) and PET (positron emission tomography). However, in CT, exposure to X-ray is unavoidable, and in PET, exposure to γ-ray is unavoidable. In recent years, by virtue of developments in performance of the apparatuses, imaging of multi-sections can be attained. However, increase in exposure dose thereby imposes a further burden to patients. On the other hand, MRI is a noninvasive diagnostic imaging method free from radiation exposure, and has an advantage in that an image of an arbitrary section can be obtained. MRI equipments make images receiving nuclear magnetic resonance signals from the hydrogen atoms contained in water, fat and other components in human body. Therefore, it is theoretically impossible to directly image a physiological action such as metabolism or to image molecules in a living body, which do not have a hydrogen nucleus, and what is actually done by the MRI equipments is nothing more than imaging of density distribution of hydrogen atoms in water. Studies of MRI progressed in the improvements and developments of imaging methods such as pulse sequence, analysis method and of the equipments. However, history of the studies on the contrast agents at a molecular level taking the principle of MRI into consideration is short, and the number of reports thereon is small.
To promote the sensitivity of MRI, MRI contrast agents are widely used. MRI contrast agents clinically and usually used now include gadolinium complex type such as Magnevist (registered trademark) and ProHance (registered trademark), and supermagnetic particle type such as Feridex (registered trademark) consisting of iron oxide (Fe2O3)m(FeO)n. However, the molecules of these contrast agents do not have a function to recognize a specific guest molecule. Even if a contrast agent is administered to the body by intravenous injection or the like, the contrast agent is not distributed to the targeted site in the body. When the supermagnetic particles are administered to the body, they are accumulated specifically in the liver due to the metabolic pathway, and are then subjected to glucuronidation and biliary excretion.
MRI probes in which a specific group is bound to the widely used gadolinium complex have been reported (Patent Literatures 1-3), which are responsive to zinc ion by coordination of the group to zinc ion. However, no gadolinium complex-based MRI probe responsive to an ion or compound other than zinc ion is known.
Non-patent Literature 1: K. Hanaoka et al., Chemistry & Biology 2002, 9, 1027-1032
Non-patent Literature 2: Wen-hong Li et al., J. Am. Chem. Soc. 1999, 121, 1413-1414
Non-patent Literature 3: Wen-hong Li et al., Inorg. Chem. 2002, 41, 4018-4024